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MikeL, ASE Certified Technician
Category: Car
Satisfied Customers: 9
Experience:  ASE master/Audi Master Guild
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2001 Audi TT: runs great with one exception..diagnostics

Customer Question

I own a 2001 Audi TT Coupe 225. I love this car and it runs great with one exception. There is a ghost in the diagnostics. Frequently, sporadically, after having driven the car at highway speed, I get a oil pressure warning light alert. The warning light comes on when I exit the parkway and come to a stop. The light will go off when I start up again. I have checked the oil level and it is always within normal levels on the dip stick. The car uses no discernible oil. Coupled with the warning light, the temperature gauge will drop from normal operating temperature to cold. It will gradually work its way back to normal. Each time the warning light comes on it drops back to cold. The car runs perfectly during these periods except for the warning light and the very annoying audible alarm. Any ideas?
Submitted: 9 years ago.
Category: Car
Expert:  MikeL replied 9 years ago.


This is a common problem on this car. It is caused by a defective coolant temperature sensor. When the sensor is acting up, the gauge gets a cold reading and will drop to cold.

When the engine is cold , the oil pressure will be high due to the oil being thicker. Because the car is actually hot, the oil pressure is lower as it should be, but since the coolant sensor is sending a cold reading the instrument cluster is expecting a higher oil pressure. So you get a false oil pressure light.

Hope that makes sense.


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Customer: replied 9 years ago.

If I understand correctly, the replacement of the coolant temperature sensor should correct this problem.

I have replaced two sensors that were faulty after the "check engine" light came on. Could this coolant temperature sensor also cause the check engine light to come on? Seems like the sensors which are supposed to alert you of a problem are themselves the problem. Thank you.
Expert:  MikeL replied 9 years ago.

Yes, a new coolant sensor should correct problem.

The check engine light will come on if the ECM sees an open circuit or a short circuit inXXXXXcycles.

But there are 2 separate sensors in the sensor housing. There are 4 pins, 2 are sensor for the ECM. The other 2 are sensor for the instrument cluster. Often 1 side fails and the other doesn't. If you have access to a scan tool that can faults in the instrument cluster, you would likely see a fault in there.